Lecture 2Dr. Zahoor Ali Shaikh

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ORAL CAVITY SALIVA SECRETION

SWALLOWING

ORAL CAVITY

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Entry to GIT is through the mouth or oral cavity.

In mouth, we have: LIPS These are muscular, help to keep the food

in mouth.Lips have non-digestive function also e.g.

help in speech, have sensory receptors.

ORAL CAVITY

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PALATE It forms the roof of the oral cavity and

separates the mouth from the nasal passages.

Palate allows breathing and chewing to take place at the same time.

At the end of palate, there is UVULA.NOTE – During swallowing one has to stop

breathing.

ORAL CAVITY

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TONGUEIt forms the floor of the oral cavity, it is

composed of voluntarily controlled skeletal muscles.

Movements of tongue help in guiding food within the mouth.

Tongue plays important role in speech. Taste buds [e.g. sweet, bitter] are located

at the tongue.

ORAL CAVITY

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PHARYNXIt is the cavity at the throat.It acts common path for both digestive

system [mouth and esophagus for food] and respiratory system [link between nasal passages and trachea for air].

In the side walls of pharynx are tonsils, lymphoid tissues, part of body’s defense.

ORAL CAVITY

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TEETHTeeth are responsible for process of

mastication or chewing. Teeth are embedded in jaw bones.Chewing helps in breaking the food into

smaller pieces to facilitate swallowing and increase food surface area where salivary enzymes can act.

Chewing helps to mix food with saliva.

SALIVA

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It is secretion produced by salivary glands.Daily secretion about 1000ml– 1500mlThere are 3 pairs of salivary glands which

produce saliva, they lie outside oral cavity and discharge saliva through ducts in the mouth. They are:

i). Parotid Glands ii). Submandibular Glandsiii). Sublingual Glands

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COMPOSITION OF SALIVA

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Water – 99.5%Electrolyte & Protein – 0.5%pH – 7Salivary protein are amylase, mucus,

lysozyme.Saliva contains two major types of protein

secretion:1. Serous secretion – contains α-amylase

[ptyalin] enzyme for digesting starch.2. Mucus secretion – that contains mucin for

protection and lubrication.

COMPOSITION OF SALIVA

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Parotid gland secrete serous type of secretion.

Submandibular gland secrete both i.e. serous and mucus secretion.

Sublingual Glands secrete mainly mucus.

COMPOSITION OF SALIVA

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Saliva is secreted in the acini is nearly isotonic to the plasma.

During passage through the ducts, the composition of saliva is modified as Na+ and Cl- are absorbed and K+ and HCO3 are secreted.

The ducts are relatively impermeable to water.

Therefore, saliva that reaches the mouth is HYPOTONIC, rich in K+, but depleted of Na+ and Cl-.

FUNCTIONS OF SALIVA

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1. Helps in digestion of carbohydrates in mouth through action of salivary amylase, an enzyme that breaks polysaccharide into maltose [disaccharide].

2. Helps in swallowing by providing lubrication due to presence of mucus.

3. Anti-bacterial action due to presence of lysozyme, an enzyme that destroys bacteria.

4. Acts as solvent for molecules that stimulate taste-buds [present on the tongue].

FUNCTIONS OF SALIVA

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5. Helps in speech [it is difficult to talk when mouth is dry].

6. Helps in oral hygiene by keeping mouth and teeth clean.

7. Saliva is rich in bicarbonates which neutralizes acids in food.

8. Prevents dental caries.

9. Saliva contain IGA

SALIVA

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Is Saliva essential for digestion?Not essential for digestion because enzymes

produced by pancreas and small intestine can complete food digestion even in the absence of salivary secretion.

CLINICALDecreased salivary secretion is called

‘XEROSTOMIA’. It causes dryness of mouth, therefore, difficulty in chewing, swallowing, speech, increase in dental caries.

SALIVARY SECRETION

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Salivary secretion increased with different stimuli.

It is maximum with lemon [4 to 5ml/min].There is continuous basal secretion of

saliva [0.5ml/min] due to stimulation of parasympathetic nerve ending to salivary glands.

Salivary secretion is increased by:(i). Simple Reflex(ii). Conditioned Reflex

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SALIVARY SECRETION

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(i). Simple Salivary ReflexWhen we take food, chemoreceptors and pressure

receptors in oral cavity are stimulated.Afferent nerve carry impulse to salivary center in

Medulla [brain stem], it send impulse via autonomic nerves to salivary glands and increase salivary secretion.

(ii). Conditioned ReflexIt occurs without taking food, but just thinking,

seeing, smelling of food.Reflex occurs through cerebral cortex to stimulate

medullary salivary center.

Control of Salivary Secretion

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Both parasympathetic and sympathetic ANS supply salivary glands and increase salivary secretion.

The quantity, characteristic, and mechanism of saliva production by parasympathetic and sympathetic are different.

Control of Salivary Secretion

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Parasympathetic – produces increased amount of watery saliva rich in enzymes.

Sympathetic – produces small increase of thick saliva, rich in mucus.

IMPORTANT – control of salivary secretion is NEURAL only [other digestive secretion are regulated by nervous system and hormones].

SWALLOWING Swallowing mean moving the food from the

mouth through esophagus into the stomach.

Swallowing is all or none reflex.Swallowing is initiated when a bolus or

chewed food or liquid is voluntarily forced by the tongue to the back of mouth into the pharynx.

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SWALLOWINGPharyngeal pressure receptors send

afferent impulses to the swallowing center located in the medulla of brain stem.

Swallowing center activates the muscles involved in swallowing.

Swallowing is initiated voluntarily but once began, it can not be stopped.

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SWALLOWINGSwallowing has three stages: 1. Oral Stage - voluntary 2. Pharyngeal Stage – involuntary 3. Esophageal Stage – involuntary

Oropharyngeal StageIt last for 1 to 2 second and consist of

moving the bolus from the mouth through the pharynx into the esophagus.

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SWALLOWING Oropharyngeal Stage {cont}When bolus [food] enters the pharynx, it is

directed into the esophagus and prevented from entering the trachea or nasal passages.

Food is prevented from entering the nasal passages by elevation of soft palate and uvula sealing off the nasal passages from the pharynx so that food does not enter the nose.

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SWALLOWING Oropharyngeal Stage {cont}Food is prevented from entering the

trachea by elevation of larynx and tight closure of vocal cords across the laryngeal opening or glottis.

Epiglottis – cartilaginous tissue prevents the food from entering the trachea.

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SWALLOWINGDuring swallowing, respiration ceases, as

respiratory passages are sealed off and swallowing center briefly inhibits the respiratory center in medulla.

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WHAT YOU SHOULD KNOW FROM THIS LECTURE

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Oral CavitySalivaSalivary GlandsComposition of SalivaFunctions of SalivaSalivary Secretion Neural ControlXEROSTOMIASwallowing

THANK YOU

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